Process of preparation of amino functionalized diene polymers, polymers of such type, rubber composition and tire casing containing those polymers

ABSTRACT

The present invention provides a process for preparing amino functionalized diene polymers with 1,4-trans linkage content equal to or greater than 70%. The invention also concerns polymers of such type, a rubber composition and a tire casing containing those polymers. The process of preparation according to the invention comprises polymerizing at least one diene monomer by means of a lithium catalytic system, which comprises at least one hydrocarbon solvent, one compound A of a IIIA group metal, one compound B of an alkaline earth metal and one aminolithium initiator C. Amino functionalized diene polymers with high 1,4-trans linkage content according to the invention are such that the amino function, situated at the end of the polymer chain, is a tertiary amino function, the rate of functionalization of said polymers being equal to or greater than 50% and the 1,4-trans linkage content being equal to or greater than 70%. A rubber composition vulcanizable with sulfur according to the invention is such that it contains at least said polymer. A tire casing according to the invention is such that it contains said composition.

BACKGROUND OF THE INVENTION

The present invention concerns a process of preparation of aminofunctionalized diene polymers with 1,4-trans linkage content equal to orgreater than 70%. The invention also concerns polymers of such type, arubber composition and a tire casing containing said polymers.

Applicant has described, in French Patent FR-A-2,294,186, a process ofpolymerization of conjugated dienes or of copolymerization of conjugateddienes, either with other conjugated dienes or with vinylaromaticcompounds. The examples of polymers obtained, which appear in thatdocument, present 1,4-trans linkage contents covering a wide range,extending from 24% to 90%.

This process consists essentially of reacting the monomers in thepresence of a catalytic composition made up of an organolithiuminitiator and of a co-catalyst. The latter comprises a barium orstrontium compound and an organometallic compound of IIB or IIIA groupmetals of the periodic classification of elements.

More precisely, said organolithium initiator can be, for example:

-   -   an aliphatic organolithium, such as ethyl lithium, n-butyl        lithium, isobutyl-lithium, sec-butyl lithium, ter-butyl lithium,        isopropryl lithium, n-amyl lithium and isoamyl lithium;    -   an alkene organolithium, such as allyl lithium, propenyl lithium        and isobutenyl lithium;    -   a living polymer, such as polybutadienyl lithium,        polyisopropenyl lithium and polystyryl lithium;    -   a polymethylene dilithium, such as 1,4-dilithiopentane,        1,5-dithiopentane and 1,20-dilithioeicosane;    -   an aromatic organolithium, such as benzyl lithium, phenyl        lithium and 1,1-diphenylmethyl lithium;    -   a polylithium obtained from an aryl-substituted ethylene        compound, the latter being, for example, 1,1-diphenylethylene,        trans-stilbene and tetraphenylethylene;    -   a radical ion, such as lithium naphthalene, lithium anthracene,        lithium chrysene and lithium diphenyl;    -   a derivative substituted by one or more alkyls.

The said barium or strontium compound is, for example, a hydride, or amono- or polyfunctional organic acid, such as an alcoholate.

As for said organometallic compound of IIB or IIIA group metals, it maybe, for example a dialkyl zinc or cadmium, a halogenated ornonhalogenated organoaluminum, an organoborium or a dialkyl aluminumhydride.

One can also cite U.S. Pat. No. 4,996,273, which discloses a process ofanionic preparation of polybutadiene having a 1,4-trans linkage contentranging between 82% and 91%, consisting of using an organolithiuminitiator, a barium, strontium or calcium compound and atrialkylaluminum compound having at least 13 carbon atoms.

It will be noted that neither the FR-A-2,294,186 nor U.S. Pat. No.4,996,173 mentions obtaining functional polymers.

Also known, from European Patent EP-A-661,298, is a process ofpreparation of diene polymers which are amino-functionalized andcomprise an alkoxysilane group. These polymers are, notably,characterized by a 1,2 linkage content ranging between 14% and 16%, thatis, by an overall 1,4-cis and 1,4-trans linkage content ranging between84 and 86%, which implies a 1,4-trans linkage content very appreciablybelow 80%, in the order of 60% at most.

This process consists, notably, of using, on the one hand, a lithiumamide base catalytic initiator and, on the other, a randomizing agentmaking it possible to control the 1,2 linkage content in the polymersprepared, and then of reacting the living polymer obtained with analkoxysilane compound.

Said initiator is, for example lithium hexamethylene imide.

As for said randomizing agent, it can be an ether, anorthodimethoxybenzene, an alkali metal complex and a phosphorous acidketone or triester, oxygenated derivatives of an alkali or alkalineearth metal, like lithium, sodium, potassium, calcium or barium, or evena tertiary amine.

All of the examples of preparation appearing in EP-A-661,298 refer toprocesses for obtaining styrene-butadiene copolymers. These processesconsist of directly adding the said initiator and the said randomizingagent to the polymerization medium, which consists of styrene andbutadiene monomers and of a polymerization solvent.

Concerning the anionic preparation of polymers containing an aminofunction, European Patent EP-A-590,491 can also be cited. This documentmentions the use of an aminolithium initiator consisting, for example,of hexamethyleneimine, notably, for obtaining styrene and butadienecopolymers presenting a narrow distribution of molecular weights. Thecopolymers obtained are characterized by vinyl linkage content of atleast 34.9%, that is, by 1,4-trans and 1,4-cis linkages equal to notmore than 65.1%, which implies an even lower 1,4-trans linkage content.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing of aminofunctionalized diene polymers with 1,4-trans linkage content equal to orgreater than 70%. The invention also concerns polymers of such type, arubber composition and a tire casing containing the polymers.

The process of preparation according to the invention involvespolymerizing at least one diene monomer by means of a lithium catalyticsystem, which consists essentially of at least one hydrocarbon solvent,one compound A of a IIIA group metal, one compound B of an alkalineearth metal and one aminolithium initiator C.

Amino-functionalized diene polymers with high 1,4-trans linkage contentaccording to the invention are such that the amino function, situated atthe end of the polymer chain, is a tertiary amino function, the rate offunctionalization of said polymers being equal to or greater than 50%and the 1,4-trans linkage content being equal to or greater than 70%.

A rubber composition vulcanizable with sulfur according to the inventionis such that it contains at least said polymer.

A tire casing according to the invention is such that it contains saidcomposition.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with this invention, it was sought to employ a newpolymerization process which makes it possible to obtain tertiary aminofunctionalized polymers at chain end and containing a 1,4-trans linkagecontent which is at least 70%.

For such purpose, according to the invention, the process of preparingamino functionalized diene polymers with 1,4-linkage content equal to orgreater than 70%, which involves polymerizing at least one diene monomerby means of a lithium catalytic system, is characterized in that saidcatalytic system consists essentially of at least one hydrocarbonsolvent, one compound A of a IIIA group metal, one compound B of analkaline earth metal and one aminolithium initiator C.

As representative examples of the A compounds used, the followingorganometal compounds can be cited:

-   -   halogenated or nonhalogenated organoaluminums such as        triethylaluminum, triisobutylaluminum, diethylaluminum chloride,        ethylaluminum dichloride, ethylaluminum sesquichloride, and        methylaluminum sesquichloride; dialkylaluminum hydrides, such as        diethylaluminum hydride, diisobutylaluminum hydride, etc.

A trialkylaluminum compound A is preferably used, the number of carbonatoms of which ranges from 1 to 12, and advantageously trioctylaluminum.

As representative examples of the B compounds used, the following bariumor strontium compounds can be cited:

H₂Ba and H₂Sr hydrides, mono- or polyfunctional organic acids offormulas (R—COO)₂Ba or Sr, R₁—(COO)₂Ba or Sr, in which R and R₁ areorganic radicals, the first monovalent and the second divalent, thecorresponding thioacids, mono- or polyfunctional alcoholates and thecorresponding thiolates; mono- or polyfunctional phenates and thecorresponding thiophenates; barium or strontium alcohol acid and phenolacid salts and the corresponding thioproducts; barium or strontiumβ-diketonates such as the reaction products of barium or strontium withacetylacetone, dibenzoylmethane, thenoyltrifluoroacetone,benzoyltrifluoroacetone and benzoylacetone; the organic derivatives ofbarium or strontium, such as those of 1,1-diphenylethylene,1,2-acenaphthylene, tetraphenylbutane, a-methylstyrene, or even thosesuch as diphenyl barium or strontium, bis-cyclopentadienyl barium orstrontium, trialkysilyl barium or strontium, and triphenylsilyl bariumor strontium; mixed organic derivatives such as phenylbarium iodide,methylstrontium iodide, barium or strontium salts of secondary amines;cetyl metals such as barium or strontium benzophenone, barium orstrontium cinname and the corresponding alkylated products as well asthe sulfur homologues; the radical ions of barium and strontium, such asthose of naphthalene, anthracene, chrysene, diphenyl, etc.

A calcium alcoholate can also be used for compound B.

A barium alcoholate is preferably used for said compound B,advantageously, barium ethyldiglycolate or barium nonylphenoxide.

As for the said aminolithium initiator C, it may be preferably a lithiumamide or a polymer obtained by anionic means which presents a C—Li bondand an amino function.

Said lithium amide preferably corresponds to formula XLi, with X in theX₁ or X₂ forms coresponding to the following formulas:

or as described, for example, in the work by T. C. Cheng, AnionicPolymerization published by the American Chemical Society, Washington,p. 513, 1981, the content of which is incorporated by reference in thepresent specification. Formula X₁ is such that R₁ and R₂ are each analkyl group independent of one another, the number of carbon atoms ofthe R₁ and R₂ set, preferably ranging from 2 to 15. As for formula X₂,it comprises a cycloalkyl group, n being a whole number, preferablyranging from 2 to 15.

Preferably, R₁ and R₂ can each be an ethyl or butyl radical or togetherform a cycloalkyl radical having 4 to 6 carbon atoms.

Also according to a preferential characteristic of the invention,initiator C is prepared in the absence of a polar agent.

Still more preferably, lithium dibutyl amide or lithium hexamethyleneimide is used for C.

According to a first embodiment of the invention, the said catalyticsystem consists essentially of a co-catalyst, resulting from thereaction product in the said hydrocarbon solvent of said compound A andof said compound B, and of the said initiator C.

According to a first working example of that first embodiment, theprocess of preparation according to the invention then comprises thefollowing stages:

-   -   in a first stage, the said co-catalyst is prepared by reacting        the two metal compounds A and B in the said inert hydrocarbon        solvent. The mixture obtained is then heated at a temperature        ranging between 20° C. and 120° C. and preferably between 30° C.        and 50° C. and for a duration sufficient to make possible the        reaction of both compounds A and B. This duration generally        ranges between 1 and 60 minutes and preferably between 20 and 40        minutes;    -   in a second stage, the said co-catalyst is brought into contact        with the polymerization medium containing, for example, one or        more monomers dissolved in a polymerization solvent;    -   in a third stage, the said initiator C is added to the        polymerization medium thus obtained, so as to react the mixture        obtained in said second stage, and the polymerization reaction        is subsequently stopped in order to obtain said polymers, which        are then functionalized by a chain-end amino function. These        polymers are recovered as known per se.

According to a second working example of that first embodiment, in whichthe said initiator C consists essentially of a polymer obtained byanionic means, which presents a C—Li bond and an amino function, theprocess of preparation according to the invention then comprises thefollowing stages:

-   -   a first stage is the same as that described for the said first        example;    -   a second stage comprises adding the said polymeric initiator C        to the premix obtained in the first stage and formed by        compounds A and B, possibly after having added an alkyl lithium        compound to improve the activity of the catalytic system. Said        alkyl lithium compound is preferably butyl lithium;    -   a third stage comprises adding the catalytic system thus        obtained to the said polymerization medium.

The temperature conditions are the same as those of the said firstexample.

According to a second embodiment of the invention, in which the saidinitiator C consists essentially of a polymer obtained by anionic means,which presents a C—Li bond and an amino function, the said catalyticsystem consists essentially of a premix of the said compounds A and C inthe said hydrocarbon solvent and of the said compound B. More precisely,said premix containing compounds A and C is added to the polymerizationmedium, and then said compound B is added to all that.

In these two embodiments of the process of preparation according to theinvention, one uses a quantity of reagents A and B such that the A/Bmolar ratio ranges between 0.5 and 5, preferably between 2.5 and 4. Onefurther uses a quantity of both reagents B and C, such that the C/Bmolar ratio ranges between 0.2 and 4, preferably between 1.5 and 4.

Furthermore, the polymerization solvent is preferably a hydrocarbonsolvent, preferably cyclohexane, and the polymerization temperatureranges between 20° C. and 150° C. and preferably between 60° C. and 110°C. The alkaline earth metal concentration of the catalytic system rangesbetween 0.01 mol.l⁻¹ and 0.05 mol.l⁻¹ and preferably between 0.03mol.l⁻¹ and 0.25 mol.l⁻¹.

It will be observed that polymerization according to the invention canbe continuous or discontinuous or even be carried out en masse. Thepolymers can be block, statistical, sequenced or microsequenced.

An amino-functionalized diene polymer with high 1,4-trans linkagecontent according to the invention is such that

-   -   the amino function, situated at the end of the polymer chain, is        a grafted noncyclic or cyclic tertiary amino function, so that        the chain end of the polymer corresponds, according to the        circumstance, to the formula:        where R₁ and R₂ are each an alkyl group independent of one        another, the number of carbon atoms of the R₁ and R₂ set        preferably ranging from 2 to 15, n being a whole number        preferably ranging from 2 to 15,    -   that the functionalization rate of said polymer is equal to or        greater than 50%, and    -   that the 1,4-trans linkage content is equal to or greater than        70%.

Such a polymer according to the invention, comprising an amino functionand presenting a high 1,4-trans linkage content, is notably intended tobe incorporated in a rubber composition vulcanizable with sulfur,containing a reinforcing filler, which can be based on a reinforcingwhite filler or carbon black filler.

Reinforcing white filler is understood to mean a white filler capable ofalone reinforcing, with no means other than a filler/intermediateelastomer matrix bonding agent, to provide a rubber composition intendedfor the manufacture of tires, capable in other words of replacing in itsreinforcing function a conventional carbon black filler of tire grade.

Such a reinforcing white filler can, for example, be made of silica.

As silica capable of being used in a composition according to theinvention, all the precipitated or pyrogenated silicas known to theexpert are suitable, with a BET surface value equal to or less than 450m²/g and a CTAB specific surface value equal to or less than 450 m²/g,with highly dispersible precipitated silicas being preferred.

Highly dispersible silica is understood to mean any silica having acapacity for disagglomeration and dispersion in a very large polymericmatrix observable by electron or optical microscopy on fine sections.The dispersibility of silica is also appreciated by means of anultrasonic disagglomeration capacity test followed by a measurement, bygranulometric diffraction, of the size of the silica particles, in orderto determine the median diameter (D50) of the particles and thedisagglomeration factor (Fd) after disagglomeration, as described inpatent EP-A-520,860, the content of which is incorporated herein, or asalso described in the article that appeared in Rubber World (June 1994),pp. 20-24, Dispersibility Measurements of prc. silicas, alsoincorporated herein by reference.

As nonlimiting examples of such preferred highly dispersible silicas,one can mention those having a CTAB surface of value equal to less than450 ml/g and, in particular, those described in European PatentsEP-A-157,703 and EP-A-520,862, or the Perkasil KS 430 silica of the AKZOcompany, the Zeosil 1165 MP and 85 MP silicas of the Rhodia company, theHI-Sil 2000 silica of the PPG company and the Zeopol 8741 or 8745silicas of the Huber company.

However, the silicas preferably suitable are those having:

-   -   a CTAB specific surface value ranging between 30 and 250 m²/g        and preferably between 60 and 200 m²/g,    -   a BET specific surface value ranging between 30 and 300 m²/g and        preferably between 70 and 240 m²/g,    -   a DOP oil absorption value less than 300 ml/100 g and preferably        between 200 and 295 ml/100 g,    -   a median diameter (D50), after ultrasonic disagglomeration,        equal to or less than 3 microns and preferably less than 2.8        microns, for example, less than 2.5 microns,    -   an ultrasonic disagglomeration factor (Fd) greater than 10 ml,        preferably greater than 11 ml and, more preferably, equal to or        greater than 21 ml,    -   a BET specific surface/CTAB specific surface ratio, the value of        which ranges between 1.0 and 1.2.

The physical state of the silica does not matter, whether it is in theform of powder, microbeads, granules or balls.

Of course, silica is also understood to mean mixtures of differentsilicas. Silica can be used alone or in the presence of other whitefillers. The CTAB specific surface value is determined according to themethod of the NFT 45007 standard of November 1987. The BET specificsurface value is determined according to the method of Brunauer, Emmetand Teller, J. Amer. Chem. Soc. 80:309 (1938), corresponding to the NFT45007 standard of November 1987.

One can also use as reinforcing white filler, on a nonlimiting basis:

-   -   aluminas (of formula Al₂O₃), such as the high-dispersibility        aluminas described in European Patent EP-A-810,258, or    -   aluminum hydroxides, such as those described in international        patent WO-A-99/28376.

According to another working example of a composition of the invention,said reinforcing filler can be carbon black.

All blacks commercially available or conventionally used in tires and,in particular, in treads are suitable as carbon blacks. As nonlimitingexamples, the N234, N339, N326 and N375 blacks can be cited.

Carbon black/silica mixtures or the blacks partially or totally coatedwith silica are also suitable for the invention.

Carbon blacks modified by silica are likewise suitable as reinforcingfiller, such as, on a nonlimiting basis, the fillers marketed by theCabot company under the “CRX 2000” name and described in internationalpatent WO-A-96/37547.

The reinforcing filler proportion can vary from 30 to 100 parts byweight per 100 parts polymer according to the invention.

It will be observed that the polymers obtained according to theinvention can advantageously be functionalized by differentelectrophilic coupling agents in order to produce a function interactivewith the aforesaid filler. One can, notably, mention, for these couplingagents, tin derivatives such as those cited in Japanese PatentJP-A-1,135,847, and amino derivatives such as those cited in U.S. Pat.Nos. 5,248,736, 5,281,671, 4,647,625 and 5,001,196.

The rubber composition according to the invention can further embrace,in standard fashion, when the reinforcing filler is a reinforcing whitefiller, a white filler/elastomer matrix bonding agent, which has thefunction of ensuring a sufficient bond, of a chemical and/or physicalnature, between said white filler and the matrix, while facilitating thedispersion of that white filler in said matrix.

Filler/polymer bonding agents can be used, for example, comprising thealkoxysilanes mentioned in European Patent EP-A-692,493.

In addition, a rubber composition according to the invention can furthercontain the other constituents and additives customarily used in rubbercompounds, such as plasticizers, pigments, antioxidants; condensationcatalysts, sulfur, vulcanization accelerators, dilute oils, etc.

The resulting composition according to the invention advantageouslypresents, in vulcanized state, improved hysteretic properties.

Such a rubber composition according to the invention is intended to beincorporated in a tire casing, with a reduction of the tire rollingresistance resulting from said improved hysteretic properties.

The aforesaid characteristics of this invention, as well as others, willbe better understood by reading the following description of severalworking examples of the invention, given by way of nonlimitativeillustration.

The term “polymer” below covers both homopolymers and copolymers, theterm “copolymer” covering the polymers each obtained from two or morethan two monomers, such as terpolymers.

Diene polymer is understood to mean any homopolymer obtained bypolymerization of a conjugated diene monomer having from 4 to 12 carbonatoms, and any copolymer obtained by copolymerization of one or moredienes conjugated with each other or with one or more vinylaromaticcompounds having from 8 to 20 carbon atoms. One can mention asconjugated diene, notably, 1,3-butadiene, 2-methyl-1,3-butadiene,2,3-di(alkyl in C1 to C5)-1,3-butadienes such as, for example,2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene,2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene,phenyl-1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene and2,4-hexadiene.

Styrene, ortho-, meta- and paramethylstyrene, the “vinyltoluene”commercial mixture, paratertiobutylstyrene, methoxystyrenes,chlorostyrenes, vinylmesithylene, divinylbenzene and vinylnaphthaleneare, notably, suitable as vinylaromatic compounds.

Two examples (1 and 2) are presented below of known processes for thepreparation of polymers with high 1,4-trans linkage content, as well aseight preferential examples according to the invention for thepreparation of tertiary amino functionalized polymers having a 1,4-translinkage content greater than 60% (Examples 3 to 8).

The inherent viscosities mentioned below were established at 25° C. in0.1 g/dl toluene solution.

EXAMPLE 1 Control Polybutadiene Prepared by Using an InitiatorConsisting of Butyl Lithium

In 100 ml of cyclohexane, one introduces 150 ml of a 0.87 M solution oftrioctylaluminum in toluene and 24 ml of a 1.56 M solution of bariumethyl diglycolate, that is, with an A/B molar ratio of approximately3.49. The mixture is heated at 40° C. for 30 minutes.

A quantity of that mixture corresponding to 1,790 micromoles of bariumis introduced in a medium containing 227.5 g of butadiene and 1.45 ofcyclohexane. A quantity of butyl lithium corresponding to a ratio of2.12 to barium ethyl diglycolate is then introduced. The medium isstirred for 45 minutes at 70° C. One then adds 10 ml of methanol and avolume of a toluene solution of4,4′-methylene-bis-2,6-ditertiobutylphenol, which volume corresponds to1.1 g of said compound. The solvent is evaporated under vacuum and aquantity of 182 g of polymer is obtained, which corresponds to abutadiene conversion of 80%.

The inherent viscosity of the polymer is 2.05 dl/g, and its Mooney ML(1+4) viscosity is 24. Its microstructure is: % 1,2 linkages 2 %1,4-trans linkages 83 % 1,4-cis linkages 15

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.21. Its average molecular weight, determined byosmometry, is 96,000 g/mol.

EXAMPLE 2 Control Polybutadiene Prepared by Using an InitiatorConsisting of Butyl Lithium

The operating method of Example 1 is reproduced, except that a quantityof trioctylaluminum and barium ethyl diglycolate mixture correspondingto 1020 micromoles of barium ethyl diglycolate is added to thebutadiene, and a quantity of butyl lithium is then added, so that thebutyl lithium/barium ethyl diglycolate (C/B) molar ratio is 2.62.

After 45 minutes of stirring the polymerization medium at 70° C., abutadiene conversion rate of 83% is measured.

The inherent viscosity of the polymer is 2.26 dl/g, and its Mooney ML(1+4) viscosity is 46.

Its microstructure is: % 1,2 linkages 3 % 1,4-trans linkages 82 %1,4-cis linkages 15

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.29. Its average molecular weight, determined byosmometry, is 136,000 g/mol.

EXAMPLE 3 Polybutadiene Prepared According to Said First Method (FirstWorking Example), Using an Initiator Consisting of Lithium HexamethyleneImide

The operating method of Example 1 is reproduced, except that, instead ofbutyl lithium, a quantity of lithium hexamethylene imide is used, sothat the lithium hexamethylene imide/barium ethyl diglycolate molarratio (C/B ratio) is 2.37.

After 65 minutes of stirring the polymerization medium at 70° C., abutadiene conversion rate of 80% is measured.

The inherent viscosity of the polymer is 2.18 dl/g, and its Mooney ML(1+4) viscosity is 38.

Its microstructure is: % 1,2 linkages 4 % 1,4-trans linkages 82 %1,4-cis linkages 14

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.27. Its average molecular weight, determined byosmometry, is 122,000 g/mol.

Analysis of the NMR¹H spectrum, which is carried out on a “Bruker AC200” spectrometer, shows at 2.95 ppm a mass spectrum attributed to theC₆H₁₂N—CH₂—CH═CH-polymer methylene group. Quantitative analysis of thatspectrum gives a function rate of 4.63 milliequivalents per kg ofelastomer which, considering the molecular weight of the polymer,corresponds to an amino function rate of 56%.

EXAMPLE 4 Polybutadiene Prepared According to Said First Method (FirstWorking Example), Using an Initiator Consisting of Lithium HexamethyleneImide

The operating method of Example 2 is reproduced, except that, instead ofbutyl lithium, a quantity of lithium hexamethylene imide correspondingto a C/B molar ratio of 2.87 is injected into the polymerization medium.

After 60 minutes of stirring the polymerization medium at 70° C., abutadiene conversion rate of 83% is measured.

The inherent viscosity of the polymer is 2.26 dl/g, and its Mooney ML(1+4) viscosity is 51.

Its microstructure is: % 1,2 linkages 4 % 1,4-trans linkages 81 %1,4-cis linkages 15

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.38. Its average molecular weight, determined byosmometry, is 146,000 g/mol.

Quantitative analysis of the NMR¹H spectrum, as in Example 3, gives afunction rate of 5.19 milliequivalents per kg of elastomer which,considering the molecular weight of said polymer, corresponds to anamino function rate of 76%.

EXAMPLE 5 Polybutadiene Prepared According to Said First Method (FirstWorking Example), Using an Initiator Consisting of Lithium Dibutylamide

The operating method of Example 1 is reproduced, except that, instead ofbutyl lithium, a quantity of lithium dibutylamide is used with a C/Bmolar ratio of 2.37.

After 65 minutes of stirring the polymerization medium at 70° C., abutadiene conversion rate of 84% is measured.

The inherent viscosity of the polymer is 1.97 dl/g, and its Mooney ML(1+4) viscosity is 22.

Its microstructure is: % 1,2 linkages 4 % 1,4-trans linkages 81 %1,4-cis linkages 15

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.26. Its average molecular weight, determined byosmometry, is 92,000 g/mol.

Analysis of the NMR¹H spectrum shows at 2.95 ppm a mass spectrumattributed to the (butyl)₂N—CH₂—CH═CH-polymer methylene group.Quantitative analysis of said spectrum gives a function rate of 7.59milliequivalents per kg of elastomer which, considering the molecularweight of the polymer, corresponds to an amino function rate of 70%.

EXAMPLE 6 Styrene-butadiene Copolymer Prepared According to the SaidFirst Method (First Working Example), Using an Initiator Consisting ofLithium Hexamethylene Imide

In 100 ml of cyclohexane, one introduces 150 ml of a 0.87 M solution oftrioctylaluminum in toluene and 24 ml of a 1.56 M solution of bariumethyl diglycolate, that is, according to the A/B molar ratio ofExample 1. The mixture is heated at 40° C. for 30 minutes.

1. A quantity of that mixture corresponding to 1,100 micromoles ofbarium is introduced in a medium containing 110 g of butadiene, 90 g ofstyrene and 1.3 of cyclohexane. A quantity of lithium hexamethyleneimide with a C/B molar ratio of 2.74 is then added. The medium isstirred for 60 minutes at 70° C. One then adds 10 ml of methanol and avolume of a toluene solution of4,4′-methylene-bis-2,6-ditertiobutylphenol, which volume corresponds to0.72 g of said compound. The solvent is evaporated under vacuum and amonomer conversion rate of 58% is obtained.

The inherent viscosity of the polymer is 1.5 dl/g and the averagemolecular weight is 110,000 g/mol.

Its microstructure is: % styrene 30

Microstructure of the butadiene part: % 1,2 linkages 3 % 1,4-translinkages 83 % 1,4-cis linkages 14

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.42.

Quantitative analysis of the NMR¹H spectrum, as in Example 3, gives afunction rate of 5.4 milliequivalents per kg of elastomer which,considering the molecular weight of the polymer, corresponds to an aminofunction rate of 60%.

EXAMPLE 7 Styrene-butadiene Copolymer Prepared According to the SaidFirst Method (First Working Example), Using an Initiator Consisting ofLithium Dibutylanide

In 100 ml of cyclohexane, one introduces, as in the previous example,150 ml of a 0.87 M solution of trioctylaluminum in toluene and 24 ml ofa 1.56 M solution of barium ethyl diglycolate. The mixture is heated at40° C. for 30 minutes.

A quantity of said mixture corresponding to 840 micromoles of barium isintroduced in a medium containing 104 g of butadiene, 96 g of styreneand 1.3 of cyclohexane. A quantity of lithium dibutylanide with a C/Bmolar ratio of 2.74 is then added. The medium is stirred for 60 minutesat 70° C. One then adds 10 ml of methanol and a volume of a toluenesolution of 4,4′-methylene-bis-2,6-ditertiobutylphenol corresponding to0.72 g of that compound.

The duration of polymerization is 23 minutes and the conversion rate is63%.

The inherent viscosity of the polymer is 1.38 dl/g and its Mooney ML(1+4) viscosity is 41. Its average molecular weight, determined byosmometry, is 140,000 g/mol.

Its microstructure is: % styrene 29

Microstructure of the butadiene part: % 1,2 linkages 4 % 1,4-translinkages 80 % 1,4-cis linkages 16

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.41.

Quantitative analysis of the NMR¹H spectrum, as in Example 5, gives afunction rate of 5.7 milliequivalents per kg of elastomer which,considering the molecular weight of the polymer, corresponds to an aminofunction rate of 80%.

EXAMPLE 8 Styrene-butadiene Copolymer Prepared According to the SaidFirst Method (First Working Example), Using an Initiator Made up ofHigh-Viscosity Lithium Dibutylanide

The operating method of Example 7 is reproduced, except that one uses aquantity of trioctyl aluminum and barium ethyl diglycolate premixcorresponding to 470 micromoles of barium ethyl diglycolate. After 33minutes of polymerization at 70° C., a conversion rate of 62.5% ismeasured.

The Mooney viscosity of the polymer is 111 and the average molecularweight, determined by osmometry, is 195,000 g/mol. A portion of thepolymeric solution is diluted with 35.5 parts of aromatic oil inrelation to the elastomer and a Mooney ML (1+4) viscosity of 51 isobtained after drying.

Its microstructure is: % styrene 29

Microstructure of the butadiene part: % 1,2 linkages 3 % 1,4-translinkages 80 % 1,4-cis linkages 17

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.43.

Quantitative analysis of the NMR¹H spectrum, as in Example 5, gives afunction rate of 3.7 milliequivalents per kg of elastomer which,considering the molecular weight of the polymer, corresponds to an aminofunction rate of 70%.

EXAMPLE 9 Polybutadiene Prepared According to Said First Method (FirstWorking Example), Using an Initiator Consisting of an AminolithiumPolymer Obtained by Anionic Means

In 100 ml of cyclohexane, one introduces 26 g of butadiene and 4,815micromoles of lithium hexamethylene imide. After 7 hours ofpolymerization at 25° C., an aminolithium polybutadiene polymer C isobtained and 100% butadiene conversion is obtained.

Then, in 10 ml of cyclohexane, one introduces 20 ml of a 1.075 Msolution of trioctylaluminum (A) in cyclohexane and 4 ml of a 1.54 Msolution of barium ethyl diglycolate (B) in cyclohexane. Said mixture isheated for 30 minutes at 40° C.

A quantity of said mixture corresponding to 91 micromoles of barium isintroduced in a medium containing 22.75 g of butadiene and 145 ml ofcyclohexane. One then adds a quantity of the polymer C previouslyobtained corresponding to a C/B molar ratio of 2.12.

After 40 minutes of polymerization at 70° C., a conversion rate of 84%is measured. The inherent viscosity of the polymer is 1.66 dl/g, itsMooney ML (1+4) viscosity is 30, the molecular weight determined byosmometry is 104,000 g/mol, and the polymolecularity index, determinedby the SEC technique, is 1.2.

The microstructure of the polymer finally obtained is: % 1,4-translinkages 76 % 1,4-cis linkages 17 % 1,2 linkages 7

The function rate, determined as in Example 3 by NMR, is 8 meq/kg,which, taking into account the molecular weight of the polymer,corresponds to a function rate of 80%.

EXAMPLE 10 Polybutadiene Prepared According to Said First Method (FirstWorking Example), Using an Aminolithium Polymeric Initiator Obtained byAnionic Means

In 25 ml of cyclohexane, a premix of 21.7 millimoles of trioctylaluminumand 6.16 millimoles of barium ethyl diglycolate is prepared. After 290minutes of stirring said medium at 40° C., a quantity of said premixcorresponding to 893 micromoles of barium and 446 micromoles of butyllithium is added in 25 ml of cyclohexane. After 10 minutes of stirringat 40° C., 1,660 micromoles of an aminolithium polymer C is added, whichis synthesized as in Example 9. A quantity of cyclohexane is injected,which is adjusted so that the total volume of catalytic solution is 60ml.

After 10 minutes of stirring at 40° C., a quantity of that solutioncorresponding to 179 micromoles of barium is injected into a mediumcontaining 145 mg of cyclohexane and 22.75 g of butadiene.

After 50 minutes of polymerization at 70° C., a conversion rate of 100%is measured. The inherent viscosity of the polymer is 1.17 dl/g, themolecular weight determined by osmometry is 70,000 g/mol and thepolymolecularity index, determined by the SEC technique, is 1.36.

The microstructure of the polymer obtained is: % 1,4-trans linkages 74 %1,4-cis linkages 18 % 1,2 linkages 8

The function rate determined by NMR, as in Example 3, is 8.9 meq/kg,which, taking into account the molecular weight of the polymer,corresponds to a function rate of 60%.

EXAMPLE 11 Polybutadiene Prepared According to Said Second Method, Usingan Aminolithium Polymeric Initiator Obtained by Anionic Means

A premix of 2 millimoles of trioctylaluminum and of the aminolithiumpolymer C synthesized in Example 9 is prepared in 65 ml of cyclohexane.After 20 minutes of stirring at 25° C., a quantity of that mixturecorresponding to 182 micromoles of aluminum is added to a mediumcontaining 145 ml of cyclohexane and 22.75 g of butadiene, and then aquantity of barium ethyl diglycolate corresponding to 91 micromoles ofbarium is introduced. After 40 minutes of polymerization at 70° C., aconversion rate of 84% is measured. The inherent viscosity of thepolymer is 1.86 dl/g, and its Mooney ML (1+4) viscosity is 30; themolecular weight determined by osmometry is 105,000 g/mol and thepolymolecularity index, determined by SEC, is 1.6.

The microstructure of the polymer is: % 1,4-trans linkages 77 % 1,4-cislinkages 17 % 1,2 linkages 6

The function rate determined by NMR (as in Example 3), is 6.85 meq/kg,which, taking into account the molecular weight of the polymer,corresponds to a function rate of 70%.

EXAMPLE 12 Polybutadiene Prepared According to Said Second Method, Usingan Aminolithium Polymeric Initiator Obtained by Anionic Means and withAnother Solvent

An aminolithium polymer C is synthesized according to the methoddescribed in Example 9, except that toluene is used as solvent and theduration of polymerization is 5 hours and 30 minutes.

A premix of 2 millimoles of trioctylaluminum and of said polymer C justsynthesized is prepared in 65 ml of toluene. After 20 minutes ofstirring at 25° C., a quantity of said mixture corresponding to 182micromoles of aluminum is added to a medium containing 145 ml ofcyclohexane and 22.75 g of butadiene, and then a quantity of bariumethyl diglycolate corresponding to 91 micromoles of barium isintroduced.

After 40 minutes of polymerization at 70° C., a conversion rate of 76%is measured. The inherent viscosity of the polymer is 1.65 dl/g; themolecular weight determined by osmometry is 94,000 g/mol and thepolymolecularity index, determined by SEC, is 1.81.

The microstructure of the polymer is: % 1,4-trans linkages 76 % 1,4-cislinkages 18 % 1,2 linkages 6

The function rate determined by NMR (as in Example 3), is 6.85 meq/kg,which, taking into account the molecular weight of the polymer,corresponds to a function rate of 65%.

The results obtained in Examples 3 to 12 according to the inventionreveal, on the one hand, a 1,4-trans linkage content greater than 70%and, on the other, an amino functionalization rate of at least 56%.

It will be observed that the anionic polymerization process, accordingto the invention, for the preparation of polymers presenting theaforesaid characteristics is employed without addition of a polar agent,which is usually intended to solubilize a lithium amide base initiator.

It will also be observed that the polymers obtained according to theprocess of the invention present a reduced viscosity, which iscomparable to the viscosities obtained with an initiator consisting ofbutyl lithium (Examples 1 and 2).

It will further be observed that the impurities in the polymerizationmedium can be neutralized by the addition of butyl lithium.

Two series of experiments are presented below, which demonstrate thisimprovement of hysteretic properties for compositions filled with silicaand with carbon black respectively.

In these experiments, the properties of the compositions are evaluatedas follows:

-   -   moduli of elongation at 10% (MA10), at 100% (MA100) and at 300%        (MA300) measured according to the ISO37 standard;    -   Scott's fracture index measured at 20° C. and at 100° C.        (breaking load in Mpa/elongation at rupture in %);    -   hysteretic losses measured at 60° C. in %;    -   dynamic shear properties: measurement made as a function of        deformation at 23° C. and at 10 Hz. Nonlinearity, expressed in        Mpa, is the difference in modulus between 0.15 and 50%        peak-to-peak deformation.

Hysteresis is expressed by the measurement of tgδ at 7% deformationaccording to the ASTM D-2231-71 standard.

First Series of Experiments: Silica Mixture:

It was sought to demonstrate in this series of experiments thecontribution, within a composition C1 (close to that of a tire tread),of a natural rubber (NR)/“BR3” polybutadiene mixture prepared accordingto the invention.

This “BR3” polybutadiene is prepared as described in the above Example3, except that one injects, on the one hand, a quantity of co-catalyticsolution corresponding to a barium quantity of 1,250 micromoles and, onthe other, a quantity of lithium hexamethylene imide corresponding to aC/B molar ratio of 2.75. After 50 minutes of polymerization at 70° C., abutadiene conversion rate of 85% is measured.

The average molecular weight of that “BR3” polymer, determined byosmometry, is 105,000 g/mol.

The inherent viscosity of that polymer is 1.67 dl/g, its Mooney ML (1+4)viscosity being 28.

Its microstructure is: % 1,2 linkages 3 % 1,4-trans linkages 79 %1,4-cis linkages 18

Analysis of the NMR¹H spectrum gives, as in Example 3, an amino functionrate of 6.7 meq/kg, which, considering the molecular weight of thepolymer, corresponds to a function rate of 70%.

A mixture of “BR1” polybutadiene prepared according to the invention andnatural rubber (NR) was used as control mixture.

This control polybutadiene is prepared as described in the above Example1, except that one injects, on the one hand, a quantity of theco-catalytic solution corresponding to a barium quantity of 1,820micromoles and, on the other, a quantity of butyl lithium correspondingto a C/B ratio of 2.2. After 45 minutes of polymerization at 70° C., abutadiene conversion rate of 79% is measured.

The inherent viscosity of the polymer is 1.88 dl/g, its Mooney ML (1+4)viscosity being 30. Its microstructure is: % 1,2 linkages 3 % 1,4-translinkages 82 % 1,4-cis linkages 15

The polymolecularity index of the polymer, determined by size exclusionchromatography, is 1.3. Its average molecular weight, determined byosmometry, is 105,000 g/mol.

The formulation of rubbers of composition C1 is as follows (parts byweight): NR/“BR1” or NR/“BR3” 80/20 ZEOSIL 1165 MP silica 50 ZnO 3.0stearic acid 2.5 N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine 2.5paraffin 1.0 sulfur 1.5 N-cyclohexyl-benzothiazyl-sulfenamide (CBS) 1.8

The rubbers according to composition C1 are subjected tothermomechanical work in two stages lasting 5 minutes and 4 minutes,respectively at an average pallet speed of 45 revolutions per minute anduntil reaching a maximum drop temperature of 160° C., while the stage ofincorporation of sulfur and accelerators is carried out at 30° on acylinder tool.

These rubbers are then vulcanized at 150° C. for 50 minutes.

The table below reports properties of composition C1 in an unvulcanizedand vulcanized state, depending on whether it contains the NR/“BR1”control polymer mixture or the polymer mixture according to the NR/“BR3”invention: C1 with NR/“BR3” C1 with NR/“BR1” Unvulcanized state ML (1 +4) at 100EC 65 61 Vulcanized state Shore 63.4 63.5 MA10 4.79 4.87 MA1001.92 1.94 MA300 2.32 2.25 MA300/MA100 1.21 1.16 Scott at 20° C.:Breaking load 23.0 23.0 Elongation at rupture (%) 500 500 Losses 60° C.17.3 18.6 (deformation = 40%) Dynamic properties (between 0.15% and 50%deformation/10 Hz) Delta G* at 23° C. 1.87 2.25 tgδ_(max) at 23° C.0.140 0.150

In conclusion, it appears that the composition C1 containing a “BR3”polymer according to the invention presents a reduced hysteresis withlow and high deformation (losses at 60° C. and tgδ at 23° C.respectively), compared to the composition C1 containing the “BR1”control polymer.

This results in a reduced heating for composition according to theinvention and, consequently, reduced rolling resistance for a tirecasing containing said composition according to the invention.

Second Series of Experiments: Carbon Black Mixture:

It was sought to demonstrate here the contribution, within a compositionC2 (also close to that of a tire tread), of the aforesaid natural rubber(NR)/“BR3” polybutadiene mixture.

The said “BR1” polybutadiene/NR mixture was used as control mixture.

The formulation of rubbers of composition C2 is as follows (parts byweight): NR/“BR1” or NR/“BR3” 60/40 N234 carbon black 54 ZnO 3.0 stearicacid 1.5 N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine 2.0(antioxidant) paraffin 1.0 sulfur 1.1N-cyclohexyl-benzothiazyl-sulfenamide (CBS) 1.1

The rubbers of composition C2 are introduced at 90° C., thermomechanicalwork is carried out up to 100° C., and then carbon black, ZnO, stearicacid, paraffin and antioxidant are added. The drop is made at 165° C.after a piston stroke at 150° C. and one proceeds to incorporate thesulfur and the accelerators.

Composition C2 is then vulcanized at 150° C. for 50 minutes.

The table below reports properties of composition C2 in unvulcanized andvulcanized state, depending on whether it contains the NR/“BR1” controlpolymer mixture or the polymer mixture according to the NR/“BR3”invention: C2 with NR/“BR3” C2 with NR/“BR1” Unvulcanized state ML (1 +4) at 100° C. 113 107 Vulcanized state Shore 65.5 68.6 MA10 5.58 6.52MA100 2.00 2.25 MA300 2.56 2.60 MA300/MA100 1.28 1.16 Scott at 20° C.:Breaking load 24.0 23.0 Elongation at rupture (%) 500 500 Losses 60° C.28 30.8 (deformation = 40%) Dynamic properties (deformation =0.15%-50%/10 Hz) Delta G* at 23° C. 1.86 3.00 tgδ_(max) at 23° C. 0.1650.185

In conclusion, it appears that the composition C2 containing a “BR3”polymer according to the invention also presents a reduced hysteresiswith low and high deformation (losses at 60° C. and tgδ 8 at 23° C.),compared to the composition C1 containing the “BR1” control polymer.

This results in a reduced heating for composition according to theinvention and, consequently, reduced rolling resistance for a tirecasing containing said composition according to the invention.

1. An amino-functionalized diene polymer having a high 1,4-trans linkagecontent and an amino function situated at an end of the polymer chain,wherein the amino function is a grafted noncyclic or cyclic tertiaryamino function, such that the end of the polymer corresponds to theformula:

wherein R₁ and R₂ are each an alkyl group, the number of carbon atoms ofthe R₁ and R₂ set ranging from 2 to 15, n being the whole number rangingfrom 2 to 15, the functionalization rate of said polymer is equal to orgreater than 50%, and the 1,4-trans linkage content is equal to orgreater than 70%.
 2. The amino-functionalized diene polymer according toclaim 1, prepared by a process which comprises contacting a dienemonomer with a catalyst system consisting essentially of at least onehydrocarbon solvent, a compound A of a group IIIA metal, a compound B ofan alkaline earth metal, and an aminolithium initiator C.
 3. Theamino-functionalized diene polymer according to claim 2, whereincompound A is a trialkyl aluminum, compound B is a barium or calcium orstrontium alcoholate, and initiator C is a lithium amide or a polymerobtained by anionic means which presents a C—Li bond and an aminofunction group.
 4. A rubber composition vulcanizable with sulfur,containing a reinforcing filler, wherein said composition comprises atleast one polymer according to claim
 1. 5. A tire casing comprising acomposition according to claim 4.